Reversible Substation in DC Traction

Abstract

In order to improve the green foot prints and also reduce the operational costs, it is currently standard practice to fit the Rolling stock of Metros railway units with regenerative dynamic braking systems. Thus, energy generated by a braking train can be reused by other accelerating trains. The excess energy is inverted back to the system for use in auxiliary power requirement like lighting lifts, escalator ect in stations. To capture the regenerative energy the popular technology in use are Energy Storage Systems (Batteries, Super capacitors and Fly wheel) and Inverters. For the urban metro rail using DC traction recently a new technology has been used which is known as the “Reversible Electric Sub Stations”. This improves the line receptivity of the DC systems by transferring the excess energy to the AC side. This new technology will make it possible to send that part of the braking energy that is usually burnt in resistors, back into the grid. That is by making the electric substation “reversible”, meaning that they can also operate in the reverse, feeding energy from the braking trains back to the grid. The main benefit is 99% of the regenerated energy is used and the braking resisters in the Rolling stock can be removed, which will in turn reduce the train mass and heat generated.